The present invention relates to a method for the preparation of branched cyclodextrins.
Cyclodextrin is an oligosaccharide formed of at least six glucose units bonded together through .alpha.-1,4-linkages and principal known cyclodextrin compounds include .alpha.-, .beta.- and .gamma.-cyclodextrins formed of 6, 7 and 8 glucose units, respectively.
Molecules of cyclodextrins have a cavity inherently due to the chemical structure thereof and the cavity exhibits hydrophobicity so that various kinds of oil substances can be incorporated into the cavity and retained therein. By virtue of this unique property, cyclodextrins have found very wide applications and are highlighted in a variety of industries for the manufacture of, for example, medicines, cosmetics and toiletries, perfumes, foodstuffs and the like.
Cyclodextrins generally have low solubility and the values are only about 14, 2 and 23 for the .alpha.-, .beta.- and .gamma.-cyclodextrins. .beta.-Cyclodextrin has a particularly low solubility and this is an undesirable and disadvantageous property when practical applications of cyclodextrins are intended.
The inventors have recently conducted extensive investigations on branched cyclodextrins to elucidate the properties thereof [see, for example, Kobayashi, et al. Starch Science, volume 30, pages 231-239 (1983)]. Reportedly, for example, the solubility of the branched cyclodextrin is 10 times larger than that of the corresponding cyclodextrin.
Accordingly, a method has been developed for the preparation of branched cyclodextrins from starch and various types of branched cyclodextrins are being produced by this method. The principle of this method is to roll in the branched parts of the starch molecules to effect the cyclization reaction so that this method is advantageous in that a variety of the branched cyclodextrins are obtained by the method. This method, however, is disadvantageous when a single kind of the branched cyclodextrin is desired.
An attempt has already been made [M. Abdullah and D. French, Nature, volume 210, No. 5052, page 200 (1966)] for the preparation of various kinds of branched cyclodextrins utilizing the reverse action of pullulanase on a mixture of a cyclodextrin and an oligosaccharide. Their works, however, are limited, insofar as in the report, to a mere observation of the reverse action of pullulanase in the paper chromatography and details have not yet been disclosed.